Heretofore, techniques for improving performance of tires have been proposed, in which a tread member is formed to have a two-layer structure including an outer surface layer and an inner surface layer having different properties. Specifically, a technique for reducing the amount of uneven wear of tires at the early stage of wear and also improving grip performance of the tires at the time of driving on an icy/snowy road has been proposed (see Patent Document 1). In this technique, a tread member is formed to have a two-layer structure in which the degree of hardness of an outer surface layer is higher than that of an inner layer. Further, a technique for improving grip performance of tires at the early stage of driving has been proposed (see Patent Document 2). In this technique, a tread member is formed so that the ratio of the stress of a rubber composition forming an inner surface layer at 300% elongation to the stress of a rubber composition forming an outer surface layer would be 70% or less, that is, the tread member is formed to have a two-layer structure in which the outer surface layer is softer than the inner surface layer.
When a tread member is formed to have a two-layer structure, uniform disposition and insertion of members each having a thickness of 1.5 mm or smaller are required. However, such a technique of uniform disposition and insertion of members having a thickness of 1.5 mm or smaller is extremely difficult from a manufacturing process viewpoint, which prevents manufacture of tire tread members with high productivity. Moreover, when the outer surface layer of the tread member is formed of a member having a low degree of hardness, the outer surface layer and the inner surface layer result in having different rigidities. Therefore, this increases the occurrence of another type of uneven wear in which only hard rubber remains selectively, at the last stage of driving. Furthermore, when the outer surface layer of the tread member is formed of a member having a high degree of hardness, an uneven wear resistance at the early stage of driving is improved while the grip performance of the tire sometimes decreases significantly.
The present invention has been made to solve the above-described problems. An object of the present invention is to provide; a pneumatic tire with excellent productivity that is capable of reducing uneven wear likely to occur at the early stage of wear while maintaining grip performance; and a manufacturing method thereof.    Patent Document 1; Japanese Unexamined Patent Application Publication No. 7-117411    Patent Document 2; Japanese Patent Application Publication No. 2002-079808